1. Field of the Invention
The present invention generally pertains to dishwasher wash arms of the rotatable type and, more particularly, to wash arms which supply a cleaning spray to a dishwasher filter.
2. Description of the Related Art
During the development of dishwashing machines, it has been common to include strategically located holes in the wash arm to supply a dish-cleaning spray to dishes or the like within the machine. It has also been common for the wash arm to include additional holes which perform a wash arm propelling function. The dish-cleaning spray is typically provided by a series of holes on the upper surface of the wash arm which are generally aimed towards the dishes to be cleaned. The propelling function is typically provided by holes at opposite terminal ends of the wash arm which are advantageously located and sized to control the rotational speed of the wash arm.
It has been proposed to orient the openings in the upper surface of the wash arm such that the propelling and dish cleaning functions are simultaneously provided thereby. U.S. Pat. No. 3,809,106, which discloses an upper wash arm including a plurality of upwardly and downwardly directed spray openings, is exemplary of wash arms of this type. The openings are arranged to provide sufficient rotational motion to the wash arm and thereby simultaneously provide both the dish washing function and the wash arm propelling function. See also, U.S. Pat. No. 3,951,684.
In recent times, wash arms have been further developed to include openings which direct a spray of wash water toward a filter to thereby rinse debris from the filter. U.S. Pat. No. 4,038,103 is illustrative of this type of wash arm. In the '103 patent, wash water from the sump is drawn through a vertically-oriented filter. Debris is filtered from wash water as it flows through the filter. Filtered debris is retained on the exterior surface of the filter. Water emanating from an opening in the wash arm impinges upon the exterior surface of the filter at an acute angle, thereby washing the filtered debris down into the sump where it will be drained from the machine at the end of the wash cycle.
A comparable filter-cleaning wash arm is disclosed in British Patent No. 2,204,482 wherein separate openings simultaneously rinse fine and course filters. The wash arm of the '482 patent produces three rinsing jets, two of which tangentially strike or impinge upon the fine filter and wash debris therefrom, while the remaining rinsing jet perpendicularly impinges upon the coarse filter. A related filtering scheme is disclosed in U.S. Pat. No. 4,972,861.
U.S. Pat. Nos. 4,392,891; 4,559,959; and 4,673,441 disclose wash arms which provide spray openings to direct a rinsing spray to impinge upon and, in effect, back-flush a filter. The filter removes debris from wash water flowing therethrough, and retains the filtered debris on an inner surface thereof. The openings in the wash arm spray wash water onto an outer surface of the filter. The filtered debris is retained within a chamber, and later drained therefrom. See also, U.S. Pat. No. 3,575,185 wherein a portion of the water to the wash arm is diverted to rinse or back flush a vertically-oriented filter.